I had the same issue, it is definitely coolant related, the level is probably low, so you more than likely have a leak somewhere. Don't just trust the overflow tank either, because you probably have an air pocket in your system, so check the radiator fluid level and you will need to vent the system when you are filling it to get all of the air out of the lines.

There will be a brass fitting in one of the hoses on top of your motor. Get the engine to operating temp and carefully loosen the brass fitting. Coolant will sputter out with the air. Once there is a solid stream you can close it. Caution: coolant exiting the bleeder valve will be extremely hot and will burn you badly so be extra careful. Also be careful when tightening the bleeder valve as it is brass and very easy to strip or break.